


The Barrier Between Worlds

by blueberrytrain



Category: Servamp (Anime & Manga), Undertale (Video Game)
Genre: Alternate Universe - Creatures & Monsters, Anime/Video Game Fusion, Black Cat is separate from Sleepy Ash, Canon-Typical Violence, Elemental Magic, Gen, I'll try to make them make sense in fanfic tho, Lawless and Kuro are the only ones who are siblings, Motherly Snow Lily, Other Additional Tags to Be Added, Threats of Violence, Undertale AU, Undertale Spoilers, Video Game Mechanics, big brother Kuro, most of the vampire characters have some/most of their demon characteristics
Language: English
Status: In-Progress
Published: 2020-10-16
Updated: 2020-10-16
Packaged: 2021-03-09 05:27:02
Rating: Teen And Up Audiences
Warnings: Graphic Depictions Of Violence
Chapters: 1
Words: 2,933
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/27039445
Author URL: https://archiveofourown.org/users/blueberrytrain/pseuds/blueberrytrain
Summary: Long ago, two races ruled over Earth: HUMANS, and MONSTERS.One day, war broke out between the two races. After a long battle, the humans were victorious. They sealed the monsters underground with a magic spell.On one fateful day, a young human boy climbs the mountain for his own mysterious reasons. Legends say that those who climb the mountain never return. The human discovered an enormous hole in the ground beneath his feet, however fell past the barrier between worlds; Landing in the Underground, alone.From then on, the story of the fallen human began to unfold.
Comments: 2
Kudos: 10





	The Barrier Between Worlds

**Author's Note:**

> It has been. 2 years. To the day. Since I have finished a Servamp fanfiction.
> 
> I've been thinking about this for a long time, and I'm happy to actually manage to get this small first chapter finished! This is mostly a test run to see if the idea is well-received, so I apologize if its a bit lackluster or something. I have some good ideas that I want to attempt to execute with this, but that's mostly if I can stay motivated enough to keep going... please have faith in me. QwQ orz
> 
> thank u sm to sara for beta editing this for me... i love u so much my Friend,

Long ago, two races ruled over Earth:

HUMANS, and MONSTERS.

One day, war broke out between the two races. 

After a long battle, the humans were victorious.

They sealed the monsters underground with a magic spell.

* * *

Many years later . . .

MT. EBOTT  
20XX

On one fateful day, a young human boy climbs the mountain for his own mysterious reasons. Legends say that those who climb the mountain never return. The human discovered an enormous hole in the ground beneath his feet, however fell past the barrier between worlds; Landing in the Underground, alone.

From then on, the story of the fallen human began to unfold.

* * *

A young boy lay still, brown hair resting softly against a patch of golden flowers. Sun rays beamed on his skin through the barrier, keeping him warm despite being beneath the Earth’s soil. His body turned on its side as he slowly came to his senses, mind hazy and desperately trying to stay conscious. He carefully sat up in the bed of unfamiliar flowers, looking around. _They must have broken my fall…_ , he thought to himself.

Patting the dirt and dust off of his striped shirt, the boy began to stand. Albeit on shaking legs and a bit dizzy from waking up, he was okay! It was definitely a good start, he supposed. He looked towards the gentle, warm sun beams; the barrier above him glinted and swirled opalescent colors, with the light shining against it from above. It looked nothing like that looking in, and he guessed that was why the legends told of so many who simply… Never came back alive. 

The reminder of such stories made him swallow thickly. Maybe their fall was something they never saw coming, the individuals being thrust into the mountain’s caves by surprise. Or did others come here on purpose, with a predetermined fate? Did they fall to their deaths, and the boy was somehow one of the lucky ones? Were they… Killed, upon walking further into the Underground? The legends told of monsters and demons hidden below, dangerous and evil, after all. Whether or not it was true didn’t change the number of ‘missing persons’ reports since before he could remember, and it was frightening. He had no idea if it was better or worse to imagine this place being completely devoid of all sentient life. It was already so lonely.

The human swallowed again. He couldn’t climb back up, and he didn’t know if it was because of the barrier itself or the distance. It was definitely better to not push his luck and risk his life.

Which meant he had to move forward, deeper into the caverns.

He gathered himself and started towards the long hallway ahead, covered in craggly cobblestone, the in-betweens of the rocks filled in with moss, weeds, and probably incredibly old soil. The sunlight from the surface no longer reached the deepest crevices looking in; the way forward was just barely visible, lit only by a few rusty torches along the walls as the fire cracked and sparkled, which he could only assume was the effects of magic. Inside the boy quietly prayed that the rest of the Underground was at the very least similarly lit, if anyone truly resided here.

At the end of the hall was an ominous, stone doorway that made him shiver slightly. Large columns made up the sides, and it was undoubtedly very old. It looked as if-with a single touch-the entire thing would collapse. A damaged emblem adorned the top, the engraved image almost resembling an angel’s wings at first glance. He’d never seen it before, not even in old history books that tell of the ancient war. It made him think, just for a moment, if maybe monsters had similar mythical stories about the surface world.

Inside the doorway was a different kind of dark, that which he’d never seen before. It was hardly even possible to make out any walls. The only lightsource was a single beam of sunlight from above, resting on a small patch of moss. The same opalescent barrier from before shone on the hole, making the sunbeams swirl and sparkle.

The boy’s heart pounded against his ribcage. The only way out was in. And so he pushed forward.

* * *

Walking into the next corridor was like depriving someone of their senses; when an area is so impossibly black that one can’t feel if they’re actually blinking, breathing, or physically feeling anything. The human moved towards the mossy patch in the center, hoping to shake off the sudden unease that filled his body the further in he went. Though somehow, the sunlight didn’t warm his skin this time. He had a deep, innate feeling that he was being watched very intensely.

_”Greetings!”_

As if on cue, a small, black animal? Doll? Monster?, emerged from the shadows beyond vision. It looked as if it had been sewn together messily, stitches connecting the limbs to its small body, but it was… Alive. It was very, very alive, moving in an animated fashion. One could probably call it cute, if it weren’t for the circumstances.

“Hello…?” replied the human, hesitantly. He watched as the doll hopped side-to-side.

_”I am Nekuro! Nekuro, the Black Cat, that is. Me-Oh-My, what a fresh face! You’re new to the Underground, aren’t you, my friend? Golly, you must be very confused.”_ Nekuro wore a wide smile on its face, and its large, round eyes gleamed cartoonishly, but it was… Empty. It was unnerving.

“...U-Um, yes. If you could point me to--”

_“Someone oughta show you how things work down here!”_

“What? N-No, please just let me pass through--”

_“I guess little ol’ me will have to do~ Heehee, ready? Here we go!”_

In an instant, the world around the human seemed to go dark, and almost as quickly as it happened, his surroundings returned; though unlike before, a very faint red aura surrounded him, and a glowing heart could be seen just in front of him where his own _real_ heart beat beneath his skin. It was strange to see, and the magic that enveloped him had a strange tingly feeling to it. It felt almost warm and gave a constant, gentle hum, and he suddenly felt more exposed than he ever had in his life, despite being fully clothed.

Nekuro bounced about from foot-to-foot, its smile growing even further across its face. It was still empty as his eyes sparkled. _“See that heart there? That is your Soul, the very culmination of your being! Of course, it starts off weak. But it can grow strong as you collect a lot of LV!”_ , it chirped happily.

“...W-What? I don’t understand,” the boy said, visibly confused at what was happening. As far as humans were concerned, magic and Souls didn’t exist beyond legends and myths. The whole idea of there being a world beneath their feet, separated only by a barely-visible barrier, was merely something the children spoke about on playgrounds, or something that their parents told them so they would behave. Magic, monsters, Mount Ebott… It couldn’t possibly all be real.

_“Oh yes! LV stands for Love, of course! You’d like some of that, wouldn’t ya? Yes yes, I’ll share some Love with you!”_

The monster winked, and giggled, but it was impossible to tell if it was laughing at the human or not. Its voice sounded crackly and filtered, as if it was talking through a speaker. But this was no toy.

_“Down here in the Underground, Love is shared through… Friendly magical spells~! Go ahead, have some!”_ It did a spin on one foot and leapt into the air fluidly; Nekuro made a cutesy ‘mwah!’ sound effect as it kissed its little black paws, and with that motion, white sparkly pellets shot out from its badly-sewn mouth. The human backed away slowly, moving away from the pale bullets. Something wasn’t right here, and he could feel it deep within his Soul.

_“Hey now, hey now~ You missed my friendship spell! That’s no fun at all. Let’s try again, shall we?”_ It did another cute dance, but this time it tossed the bullets into the air like it was confetti. Nekuro gave another deep laugh as it traveled at him faster, and the human quickly moved out of the way to avoid being touched by the unknown power.

_“Oh, my… Are you stupid? Brain-dead? This is pretty straight-forward, you know. I already told you, it's friendly! Soak it up, now!”_

More magic, faster again. Sweat started to bead on the human’s forehead as he realized what was happening, and he tried his best to avoid it carefully. His heart was starting to beat heavily against his ribcage, unsure of what to do beyond this if things escalated.

Nekuro’s bouncing started to slow, until he stood still, staring up into his eyes. It was still an empty, cold smile, and his eyes were a hollow blackness like no other. _“Heehee… Oh my. You know what’s going on here, don’t you?”_

Suddenly the plush body melted into the stone floor in a black, thick puddle of darkness; the amalgamation then began to rise until it towered over the human’s entire being, and its stare bore into his heart and Soul with a terrifying face. The magic around them now crackling was filled with malice, the tension thick. It was so hard to breathe, and he knew it wasn’t just because he was in the Underground; the darkness around him - whatever it was made of - was almost suffocating him completely, yet he tried to gulp in breaths in pure terror. He whimpered as he looked at the monster before him and fell backwards, the sludge beneath him splattering, yet also feeling like nothingness between his quivering fingertips.

_“You just wanted to see me suffer…”_ The voice that was once eerily cheery and static-filled was now angry, surrounding the boy’s brain in all possible directions. It was so distant yet so close, so loud yet so quiet, and he wanted to cover his ears and just hide from the grating sound. It was like glass on his eardrums now, and it felt as if it would never end.

“N-No…! Please, stop…!”

Maybe accepting this fate would be easier.

**_“You worthless human… Die.”_ **

Nekuro ripped its mouth open, the stitches popping from the friction with an almost sickening noise, and the human screwed his eyes shut. This was it. He was going to die here, alone, in the realm of the monsters.

…

…

“That’s enough!”

... 

...What?

Suddenly, as fast as he could open his eyes and blink away the static, Nekuro’s mass was blasted with a bright light and the suffocating body of darkness began to shrink away and deform, the sludge surrounding his lower body on the ground seeping into the cobblestone slowly. It was like it was being melted away by whatever magic was being fired, but it wasn’t hot. It was soft and warm, not unlike when your favorite blanket was pulled fresh out of the dryer on a particularly cold night, and you’re reminded of why the place you reside in is called “Home”. It felt comforting compared to the frightening power Nekuro was attempting to harm him with.

The terrifying form now completely faded away, Nekuro’s weakened plush self retreated to the darkness in an effort to run away from whoever attacked it. Carefully looking up from his spot on the ground, the human could see another monster before him, standing in the patch of moss covered in sunlight from above. This monster had a softer presence, and looked determined to help him, unlike the monster before. “What a terrible creature, torturing such a poor innocent youth,” the monster began. The human sitting was still visibly afraid despite the new, gentle face, and it could sense this. “Ah… Don’t be afraid, my child! My name is Lily, and I am the caretaker of these Ruins.” He gave a soft smile, and held out his hand, offering both assistance and comfort. 

“U-Um… Hello, Lily,” the human boy gave a hesitant response, but nonetheless took the hand given to him, “m-my name is Mahiru.” His voice was so quiet. It almost felt like he wasn’t truly saying the words himself.

“Mahiru… What a lovely name that is. You are the first human to fall down here in quite some time, my child. I pass through here everyday to see if someone has fallen, but it is not often that I find someone…” Lily almost looked solemn at that statement. Mahiru slowly stood, and dusted off his clothes with shaking hands. “Please tell me, are you alright?”

“Y-Yes, thank you. I don’t remember much… Besides that I woke up in a bed of flowers. I followed the torches through the halls, and then…,” Mahiru shuddered as he trailed off. Nekuro was definitely a chilling first-impression to the Underground. With Lily suddenly helping him, he now supposed it couldn’t be all bad, but this was entirely new territory. He knew he needed to tread carefully despite the kind eyes and gentle smile pointed his way, even if he initially wanted to trust him.

Which made Mahiru take a short pause to take in what he was looking at. Now that he wasn’t completely frozen in shock, he gave the monster in front of him a quick once-over. Lily’s expression was soft, but he knew he would otherwise be a terrifying force if angry. His eyes were a striking black where there would otherwise be whites, and his irises were a light red, almost pink in color. Mahiru knew such a pigment was unnatural in humans, and he quickly thought that it was unfortunate; the color itself was beautiful as Lily’s eyes glistened in the opalescent sunlight from above. A black diamond pattern ran from his eyes like tears upon his cheeks, despite being seemingly happy. Lily had blond hair in a comfortably styled bob-cut, and on top of his head sat two antennae--not unlike that of a butterfly--gently twitching as he spoke. Mahiru smiled at the sight, how curious. Dangling through his soft hair were earrings of the same color as his eyes, as well as a pristine white scarf sitting upon his shoulders and a beautiful golden pocket-watch locket beneath it. His robes were black and pink, and looked oversized yet comfortable, and Mahiru assumed that it was simply something Lily preferred. If someone had told him it was a comforter blanket, he wouldn’t even second-guess it. Not that he would judge it either way.

“Do not worry about that disgusting creature. Had I been here before, he would not have attempted to harm you. I cannot stand those who hurt my children, and though I have not known you for very long, I would never allow harm to come to you in such a way,” Lily spoke. He nodded, Mahiru guessed to himself, and brought his hand back out to the human. “Come! Let me guide you through the catacombs.”

When their palms met, Lily swung his free hand in the air above them as if he was casting a spell, and suddenly the human’s Soul began to glow once more, fading away into his body with a comforting rush of magic. Oh, right. He’d completely forgotten it was exposed from Nekuro’s unprovoked death threat. Knowing it was returned to his body, and being hand-in-hand with Lily, Mahiru instantly felt less anxious about being beneath the mountain. Maybe his journey was looking up, after all.

“This way, my child.”

Mahiru‘s hand gently squeezed the other, and he gave a small smile to affirm that he was as ready as he could ever be. Lily seemed to pick up on his anxiety before walking, and they started very slow as Mahiru collected himself. Together they bounded towards another archway, the same emblem of wings adorning the top, stone pillars looking about ready to collapse. Considering everything that had happened thus far, Mahiru simply assumed they were being cared for with a gentle hand and some even gentler magic. Lily was very motherly even to old rocks, it seemed.

Passing through the arched door, the next room was immediately less worrying upon first-glance. Light filled the room via torches lining the walls, and vines covered the stones through their cracks; though they looked purposely placed for decoration as they were obviously being maintained. There were stairs flowing up to another level, leading to another doorway. It almost looked like an old castle, rather than some random dimly-lit, broken down hallway like before. It was an extremely nice change of pace knowing he’d be able to relax as he traveled alongside Lily, and he quietly hoped this luck would keep up. 

Dead leaves surrounded the stairs leading to the entrance, and within them, Mahiru could see a sparkling _something_. He wasn’t sure what it was exactly, but he felt compelled to approach it. In any other circumstance, he’d be wary of such a thing considering his last encounter, but there was something about the shining object that was calling to him. It made his heart start to pound in anticipation.

He touched the sparkling something, and he felt a burst of energy surround him. He felt invigorated and ready; for what exactly, he was yet to find out. He looked around with this newfound feeling deep in his Soul, making him almost vibrate from the intensity of it.

The shadow of the Ruins loomed above him. For the first time since landing in the Underground, the realm of the monsters, Mahiru was filled with determination.

**Author's Note:**

> thank you for reading!!
> 
> please let me know what you think, and if you'd like to see me continue this!  
> in the meantime, if you have any questions about the AU or just want to talk about it (or anything really!), my tumblr is madburnishes!  
> (i dont know how to link in ao3... oops)
> 
> thank yooouuuuu ;___;


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